I'm looking to return to work following maternity leave and want a part time role. I'd like to approach some employers directly (for unadvertised roles), do I need to state initially I'm looking for part time or should I wait until after meeting with them?
You should say so right away, but that shouldn't be the only thing you say. In your initial contact give details of your experience and the type of work you want to do. Explain why you are attracted to their organisation. Explain that you would like a job that is part-time, but you wouldn't be opposed to increasing your hours in a few years' time (if this is true).
In short, you don't want the requirement to be easily missed, but you don't want it to be front and centre. Even if they don't have anything for you right now, you will have made a good impression.
You will save both yourself and them a significant amount of time if you state this immediately.